The Clark Bridge is located near the starting
point of the Lewis & Clark Expedition at the confluence of the Mississippi
and Missouri Rivers. A sister bridge just down the road, the Lewis
Bridge, carries US-67 over the Missouri River.

A 1928 era bridge crossed the Mississippi at Alton, just north of Saint Louis,
but the narrow twisty 2 lane bridge was inadequate. It also had a number
of short spans that required piers in the middle of the shipping lanes, which
became an even bigger problem when the nearby lock and dam was expanded.

The Clark Superbridge is an impressively large cable stay bridge, featuring two
towers that are each 250 feet tall, and extend up to 150 feet below the
water level. These stats have lead folks to refer to this structure as
the Superbridge. In fact, PBS made a TV mini-series about the building of
this bridge called Super Bridge.

The Clark Superbridge is unique in two respects. First, it has cables that
connect to both sides of the deck, but are gathered at one point on
top of the bridge. The cables form two planes that intersect. On most
cable stay bridges with two planes of cables, the towers have two different
points where the cables are mounted, and the cable planes remain parallel.
Put another way, most cable stay bridges with cables on both sides of the
deck have towers that from large 'H' figures, whereas the cables form an
inverted 'V' on the Clark Superbridge. Second, most cable stay bridges have
the cables mounted to the towers. On the Clark Superbridge, the top of the
tower is a saddle, and the cables go up and over rather than joining to
the tower. While this is an innovative design, the saddle design has
proven to have a serious problem, and is not likely to be attempted again
in the near future.